adding shower in basement

I've had a basement rough-in put in place in 1994 (refer to drawing below). It consists of a sink drain (also connected to a vent), which is connected to a toilet drain. The toilet drain is connected to a sewage tank of ~26" dia. x 3' deep, which is also vented. This sewage tank is for a future lift station (there's no sewage pump yet). The actual septic tank is outside the house but higher than the basement. All the drains are under the basement concrete floor.This rough-in passed inspection.

Note that although the picture shows the toilet and the sink, these are not present. Everything is roughed-in i.e. there's no walls yet, no ceiling, therefore the 2 existing vents are easily accessible.

I would like to add a shower which was not part of the original rough-in. This will require breaking the cement floor and adding a pipe with â€˜Pâ€™ trap.

Can I bring the pipe directly from the shower to the sewage tank ?
I will need to drill a hole on the side of the sewage tank, and connect and seal the pipe around it.
If so, do I need a vent since the pipe length will be only ~25" between both â€˜open-airâ€™ ends and since this will be a stand-alone pipe (no other pipes will be connected to it, therefore no siphon problems cause by the other drain).

Or, do I need to connect it to the existing drain (assuming that no more than one drain can go to the sewage tank) ? In this case, I do understand that I would need to vent it, to prevent siphon problems when flushing the toilet.

In our neck of the woods we are required to have vent from the sewage
pit sepretly out the roof.your codes may be different. I would tie in to
the line coming w/c.Also Iwould revent the shower drain.This should be
done in 2" pipe.A 2" ejecter pump is required.Vent from s/d can be 1.5".
Check your local codes.

all that really needs to be done is dig the line to either theside of the pit or to the 3 inch line from the toiletand then right back behind the shower throw a 2 inch wye on its back for a re-vent for the shower

thenrun that new 2 inch vent up 36 inches and tie back into the main vent comming out of the sweage pit.. that is more than large enough toaccomidate it

It does looks like a closer run just to tie into the side of the pit with a 2 inch line, but if their is a lot of SURFACE WATER and your hole is not selaed tightyou could end up with that water eventually leaching into the pit...